This invention relates to two-stroke cycle internal combustion engines wherein a complete operating cycle is accomplished during a single rotation of the engine crankshaft. In other words; the phases of compression, ignition, expansion, exhaust, and induction are all accomplished during the extension and retraction strokes of the piston. More particularly the invention relates to a unique two-stroke engine design that minimizes valving and eliminates the need to provide lubricating oil with the fuel supplied for combustion. At the same time the engine of the invention has a low level of discharged gaseous pollutants.
Two-stroke cycle internal combustion engines have traditionally had certain advantages over four-stroke cycle engines for many applications. The advantages have included a greater output per unit of weight because a power stroke occurs during each crankshaft revolution. On the other hand, prior art two-stroke cycle engines suffer from a requirement that lubricating oil be mixed with the fuel. The result is that some lubricating oil is burned and undesirable gaseous pollutants and smoke are produced. Also in prior art designs the exhausting of gaseous combustion products is often incomplete.
In typical prior art designs a fuel/air mixture is introduced through the crankcase and ported to the combustion chamber through an inlet valve. This requires that the lubricating oil be mixed with the fuel or otherwise injected into the fuel/air mixture.
Prior art two-stroke engines also usually require extensive valving to control fuel/air induction and discharge of exhaust gases. Typically the induction of the fuel/air mixture must overlap the discharge of exhaust gases through an exhaust port and this may result in either incomplete exhausting of combustion products or a more complete exhausting combined with the further exhausting of a portion of the unburned fuel/air mixture being introduced into the combustion chamber. These factors result in a high level of gaseous pollutants and reduced fuel efficiency.
Another problem encountered in prior art engines is sometimes referred to as piston scuffing. This occurs in some engines where the piston itself is connected directly to a connecting rod by a wrist pin. As a result, certain forces acting on the piston produce side loads between the piston skirt and cylinder wall. These side loads can produce scuffing as the piston traverses the cylinder wall exhaust and bypass ports.
While some more recent techniques have improved exhaust scavenging through the use of the fuel/air charge, this also results in the loss of fuel and thus lower fuel efficiency.
The device of the present invention, however, reduces the difficulties described above and provides other features and advantages heretofore not obtainable.